The cases where products are assembled using casting materials have increased in many industrial fields including the automobile industry. For example, cast components produced using aluminum die-casting are used as, for example, automobile parts such as an engine.
In a cast component, voids among the particles may remain inside the component even after the sinter-molding resulting in formation of blow holes. The texture is dense in the portion close to the surface of the cast component and no blow hole is therefore exposed. The cast component may however be finished by cutting to improve its dimensional precision and its flatness after the molding and, in this case, the blow holes inside the cast component may be exposed in the surface by the cutting to form recesses caused by the blow holes.
When such recesses are formed in the counterpart sealing face of a gasket, a problem arises that the sealing properties by the gasket cannot sufficiently be achieved. In the gasket, a bead portion is deformed to be crushed by being compressed by bolt axial forces between two members and the stress generated in the bead portion at this time seals the counterpart sealing face. In this case, when a recess is present to extend over the contact face with the bead portion, the fluid to be hermetically accommodated may leak through the recess.
Countermeasures are taken against this problem such as hermetically sealing a gap between the counterpart sealing face and the gasket by applying a resin or a liquid rubber (FIPG) to the counterpart sealing face, and changing the cast component itself to a component having a configuration with less influence of the blow holes. With the downsizing and weight reduction of the products in recent years, however, product shapes difficult to mold have increased resulting in the difficulty in the work to control the blow holes for the cast components. Application of ideas to the gasket itself is therefore also demanded as the countermeasures against the blow holes.
Such sealants have traditionally been proposed as a sealant whose clamping width is made even by disposing a recess in a portion of the circumference of its cross section to prevent the twisting and the like generated during the attachment (Japanese Laid-Open Patent Publication No. 10-318373), a sealant whose cross section is set to have a trifurcate shape to facilitate reduction of the load, reduction of fluctuation of the load, and the like (Japanese Laid-Open Patent Publication No. 2000-356267), and a sealant whose cross section is set to have a trifurcate shape to facilitate improvement of the attachment property, improvement of stability of the posture for attachment, and the like (Japanese Laid-Open Patent Publication No. 2003-322257). However, as far as these sealants are concerned, nothing is taken into consideration for these sealants concerning the countermeasures against the case where the condition of the counterpart sealing face is degraded due to the formation of the recesses by the blow holes, and the like.
Gaskets have been proposed each as a gasket for which a countermeasure has been taken against the degraded condition of the counterpart sealing face (Japanese Laid-Open Patent Publication Nos. 2003-322257 and 2011-94667) that are each enabled to cover the protrusions and recesses by forming a wide contact width for the counterpart sealing face by forming an arc portion having a small curvature and having a shape convex toward the counterpart sealing face that has a recess formed therein. These gaskets are however each formed by a rubber-like elastic body and are each not a metal gasket having a bead portion formed on a metal substrate.